Fixture for shape-sensing optical fiber in a kinematic chain

Abstract

Localized strain is effectively eliminated in a shape sensing optical fiber where the fiber exits a link in a kinematic chain. In one aspect, the fiber is positioned in a channel within a fiber fixture portion of the link, and a surface of a lip of the channel is curved. The curved surface of the lip begins tangent to a wall of the channel and has a maximum radius of curvature that is less than the minimum bend radius that the fiber will experience during shape sensing. In another aspect the fiber is positioned within a shape memory alloy tube that extends from the link.

1. An apparatus comprising:
 a first link, a second link, and a joint that couples the first and second links; 
 an optical fiber extending between the first link and the second link, wherein a limit range of motion of the joint defines a minimum bend radius of the optical fiber; and 
 a fixture by which the optical fiber is constrained with reference to the first link, wherein the fixture comprises a channel defined therein in which the fiber is positioned to place a length of fiber containing fiber Bragg gratings adjacent a lip of the channel where the channel opens out of the fixture, wherein a curve of a surface of the lip begins effectively tangent to a wall of the channel, and wherein the radius of curvature of the surface of the lip that substantially intersects a bending plane of the fiber as the joint moves is effectively less than the defined minimum bend radius of the optical fiber. 
 
     
     
       2. The apparatus of  claim 1  further comprising:
 a strain interrogator; 
 wherein the strain interrogator receives strain information from the fiber Bragg gratings. 
 
     
     
       3. The apparatus of  claim 1 :
 wherein the optical fiber extends out of the first link at the longitudinal centerline of the first link. 
 
     
     
       4. The apparatus of  claim 1 :
 wherein the optical fiber extends out of the first link offset from the longitudinal centerline of the first link. 
 
     
     
       5. The apparatus of  claim 1 :
 wherein the fixture comprises a first piece and a second piece positioned within the first piece; and 
 wherein the channel defined in the fixture is defined in the second piece. 
 
     
     
       6. The apparatus of  claim 1  further comprising:
 a flexible tube surrounding the optical fiber. 
 
     
     
       7. The apparatus of  claim 1 :
 wherein the channel comprises a slit having a width that is approximately equal to the diameter of the fiber. 
 
     
     
       8. The apparatus of  claim 1 :
 wherein the channel comprises a cylinder that permits the fiber to slide longitudinally with reference to the first link. 
 
     
     
       9. The apparatus of  claim 1 :
 wherein the channel comprises a cylinder that permits the fiber to roll or twist with reference to the first link. 
 
     
     
       10. The apparatus of  claim 1 :
 wherein the fixture comprises a collet having the channel and the lip defined therein. 
 
     
     
       11. The apparatus of  claim 1 :
 wherein the first and second links are links in a surgical instrument. 
 
     
     
       12. A method comprising:
 assembling a first link, a second link, and a joint that couples the first and second links; 
 extending an optical fiber between the first link and the second link, wherein a limit range of motion of the joint defines a minimum bend radius of the optical fiber; and 
 constraining the optical fiber with reference to the first link, wherein the optical fiber is positioned in a constraining channel to place a length of fiber containing fiber Bragg gratings adjacent a lip of the channel, wherein a curve of a surface of the lip begins effectively tangent to a wall of the channel, and wherein the radius of the curve of surface of the lip that substantially intersects a bending plane of the fiber as the joint moves is effectively less than the defined minimum bend radius of the optical fiber. 
 
     
     
       13. The method of  claim 12  further comprising:
 interrogating the fiber Bragg gratings for strain information. 
 
     
     
       14. The method of  claim 12 :
 wherein the optical fiber extends out of the first link at the longitudinal centerline of the first link. 
 
     
     
       15. The method of  claim 12 :
 wherein the optical fiber extends out of the first link offset from the longitudinal centerline of the first link. 
 
     
     
       16. The method of  claim 12 :
 wherein constraining the optical fiber comprises positioning a second piece within a first piece and positioning the fiber within the second piece; and 
 wherein the channel is defined in the second piece. 
 
     
     
       17. The method of  claim 12  further comprising:
 wherein the channel comprises a slit having a width that is approximately equal to the diameter of the fiber. 
 
     
     
       18. The method of  claim 12 :
 wherein constraining the optical fiber comprises permitting the fiber to slide longitudinally with reference to the first link. 
 
     
     
       19. The method of  claim 12 :
 wherein constraining the optical fiber comprises permitting the fiber to roll or twist with reference to the first link. 
 
     
     
       20. The method of  claim 12  further comprising:
 configuring a collet with the constraining channel and the lip. 
 
     
     
       21. The method of  claim 12  further comprising:
 positioning a flexible tube around a length of the optical fiber. 
 
     
     
       22. The method of  claim 12 :
 wherein the first and second links are links in a surgical instrument. 
 
     
     
       23. The method of  claim 12 :
 wherein constraining the optical fiber comprises allowing the optical fiber to slide longitudinally with reference to the first link. 
 
     
     
       24. The apparatus of  claim 6 :
 wherein the flexible tube surrounding the optical fiber comprises a shape memory alloy. 
 
     
     
       25. The apparatus of  claim 24 :
 wherein the shape memory alloy comprises a Nickel/Titanium alloy. 
 
     
     
       26. The method of  claim 21 :
 wherein positioning a flexible tube around a length of the optical fiber comprises positioning a shape memory alloy tube around a length of the optical fiber. 
 
     
     
       27. The method of  claim 26 :
 wherein the shape memory alloy comprises a Nickel/Titanium alloy.